Plug valves are standard available products which are designed for a number of applications. The particular invention of this application is involved with the metal sealing means for a heavy duty plug valve which is utilized in oil field operations.
Typically a plug valve includes a hollow valve body which contains a rotatable plug valve element where the plug valve element typically is rotatable through a 90.degree. (1/4 turn) for a rapid full open or closed operation. Typically, the pressure seals which are utilized to seal the trunnions and closures in a plug valve are made of elastomers such as a butadiene-styrene composition such as Hycar or a synthetic rubber such as VITON which are satisfactory for most applications. However, in some instances metal-to-metal seals would be preferable in a plug valve because of resistance to corrosive nature of fluids and resistance to temperature effects which causes deterioration of elastomer products. In the case of fire or excessive temperatures, elastomer seals in a valve can melt or soften to an extent that there is a leak and can create a fire hazard. Additionally, in a plug valve, the rotation of the trunnions relative to the seal tends to eventually wear out the seals.
Metal-to-metal seals have heretofore been employed in pipe couplings for interconnecting to flanges to one another. Current metal-to-metal seals in this type of use include the following.
(1) The API flange - this is a widely used coupling for high pressure fluids and involves a face-to-face coupling of flanges with an interposed metal sealing member between the flanges. The metal sealing member is usually a flat faced seal that is crushed between two flat faced hubs on the flanges.
(2) A "Grayloc" type connector - this connector is comprised of facing, metal seal ring, hubs and an annular clamp assembly and internal metal sealing ring resembling an inverted "T" in cross section disposed between the hubs. The clamp assembly fits over the outer annular surface of the two facing hubs and is forced radially inward by making up the clamp bolts to draw the facing hubs together and to compress with the sealing ring rib between the hub surfaces. As the hubs are drawn together by the clamp assembly, the internal seal ring lips engage and deflect against the inner sealing surfaces on the hubs. The deflection of the seal ring lips elastically preloads the lips of the seal ring against the inner sealing surfaces of the hubs thereby forming a preloaded seal. In use, internal pressure acts on the seal ring lips so that the sealing action of the lips is both preloaded and pressure-energized. However, if the internal pressure becomes sufficiently great to cause the facing hubs to be displaced or moved longitudinally of one another, the seal ring lips will lose their sealing ability because the preloading sealing compression between the hubs and the seal is lost. Also, the metal seal ring has a 20.degree. (sometimes 25.degree. ) bevel so that the seal lips do not radially compensate for movement of the seal lips when the hubs are spread apart from one another.
(3) "Weco" wing union --this coupler has metal-to-metal compression seals disposed between connector surfaces and uses a lip type elastomer replaceable seal to protect the metal primary seal.
(44) A "dynetor" connector--this is a metal-to-metal connector coupling with a reusable annular metal seal. The annular metal seal has cylindrical ends so that some longitudinal expansion or spreading between the coupling parts can occur without losing the seal in the annular seal bores.
(5) The Nicholson flange--this is an annular shaped gasket which is used between flanges and flange grooves. The flange seal, when compressed between flanges, will expand with longitudinal movement but the seal will fail because the gasket expands longitudinally and thus will fail at the gap.
(6) The Nicholson flange--this is a seal which depends upon point contact for sealing and is a round seal.
(7) The Cameron AX or CX gasket illustrated in the 1990-91 Composite Catalog, pg 696. The AX and CX gasket is a tubular member which has an external taper on each end and sealing means which engage tapered surfaces in adjoining connectors.